Whereas the feeding of saturated fats and cholesterol to the rat and several other species does not produce a marked change in the circulating lipid levels, this does occur in man and is an apparent cause of atherosclerosis. The Mongolian gerbil appears to be a useful animal model for studies in this area because it more nearly duplicates the response seen in man and it is small, docile and easy to breed. The gerbil differs from rats in its nutritional requirements. We have shown that feeding saturated fat induces an inositol deficiency which is manifest by the development of an intestinal lipodystrophy. This lesion appears to be related specifically to the feeding of saturated fatty acids containing 10 to 16 carbon atoms. Clearly saturated fatty acids of varying chain length have different effects upon mechanisms of fat transport and the literature suggest they have different effects in a variety of other biologic systems. The major objective of this research is to define the effects of different fats, fatty acids, cholesterol, carbohydrate and inositol upon lipid metabolism, especially the lipid transport mechanisms through the intestinal cells. A most useful technique for studying fat absorption is to investigate the output in lymph after administration of materials of interest. Because of the small size of the Mongolian gerbil we have been unable to do this. A larger species, M. lybicus, weighing 200 g appears to react similarly to dietary modifications and we propose to develop a small colony of these for this purpose. Finally, although the gerbil survives on purified diets adequate for the rat, they grow poorly and clearly differ in nutritional needs other than the inositol requirement.